This project will investigate whether HMO patients who transfer into an academic hospital-based practice from a community-based practice are more severely ill and/or use significantly more health care resources. The stud will determine whether a previously unidentified form of adverse selection -- within an HMO exists, and will assess its impact on hospital finances, case management and continuity of care. Enrollment and utilization data fro HealthPASS, a mandatory medicaid IPA-model HMO in Philadelphia, will be collected and analyzed in order to address the following questions: 1) do HealthPASS patients who transfer into an academic hospital-based practice from a community-based practice use more care and have more serious or resource-intensive health problems than do patients who maintain enrollment with a community-based practitioner or who initially chose that hospital-based practice?; 2) are diagnostically-defined patient subgroups (e.g. AIDS or obstetrics patients) more likely to transfer into a hospital-based practice, and do they experience resource-intensive episodes of care shortly thereafter?; and, 3) are patients who disenroll from hospital-based practices less frequent utilizers of care, perhaps following an initial resource-intensive episode of care? The HealthPASS patient panel of two large academic hospital-based primary care practices will be examine in depth. Detailed data on enrollment and service utilization will be obtained from the Pennsylvania Department of Public Welfare, an supplemente by data collected from the participating practices. The analysis will exami e differences between transfers and ongoing hospital and community-based grou s with regard to demographic and diagnostic characteristics, utilization of specific primary care, specialty consultation, and inpatient services, tota charges for car time to first hospitalization, and severity of illness, as measured by computerized disease staging and case-mix index. While many studies have examined selection between competing forms of insurance and HM plans, none have looked at patient selection differences among alternative practice forms participating in one IPA-model HMO. The possibility that patients transfer into teaching hospital-based practices in anticipation of resource-intensive episodes of care, or, are encouraged to do so by community-based practitioners, needs to be explored.